The present invention relates to the field of communications, and more particularly, to an antenna for use in portable radio communications utilizing a satellite and in portable radio communications established between ground radio stations. Further, the present invention relates to a portable radio using the antenna.
In recent years, the conception of a portable telephone using a satellite has been proposed. A frequency band of 1.6 GHz is assigned to communications from a ground portable telephone to a satellite, and a frequency band of 2.4 GHz is assigned to communications from a satellite to a ground portable telephone. The frequency band of 1.6 GHz is also assigned to bidirectional communications between the ground and a satellite.
Frequency bands of 800 MHz, 1.5 GHz, and 1.9 GHz have already been assigned to ground communications. With regard to a shared antenna used for both satellite communications and ground communications, it has been proposed a method of feeding power to the upper end of a two-wire helical antenna which uses a coaxial line and lead wires (Unexamined Japanese Patent Publication 9-219621).